A wide variety of safety devices have been used in firearm designs in order to reduce the chance of an unintended discharge. Some safeties are internal and prevent discharge if, for example, the firearm is dropped. Other safeties are external and may be “passive” or “active.” An active safety requires the user to perform a specific operation to disengage the safety, such as sliding a member, moving a lever, or rotating a selector switch. Passive external safeties include devices on the trigger or grip which are automatically deactivated when the firearm is properly held and the trigger is intentionally pulled. Some firearms include a combination of more than one internal, external, passive, or active safety devices.
A grip safety is a lever or other member situated on the grip of a firearm which must be displaced by the operator's hand, as a natural consequence of holding the firearm in a firing position, in order for the firearm to fire. The function of a grip safety is momentary in that the safety is deactivated only while the shooter maintains a proper hold on the grip and is reactivated automatically preventing discharge when the shooter releases it. The safety thus prevents discharge of the firearm in the absence of a proper, safety disengaging, grip.
A “single action” firing mechanism is one in which the hammer or striker is fully cocked and only a pull of trigger is necessary to cause it to discharge. Single action firearms are more likely to use an external manual safety to prevent accidental discharge. Some single action firearms, such as the M1911 pistol, also include a grip safety for added protection. A typical AR platform firearm, such as an AR15-style firearm, including the M16, M4, pistol configurations, and (other variants), has a single action type firing mechanism and employs only an active, external safety that is manually manipulated between “safe” and “fire” positions. If the manual safety is actively deactivated (selector switch set to “fire”), a loaded AR15-type firearm will discharge if the trigger is actuated, even if the operator is not properly gripping the firearm in a shooting position.
The use of passive safeties may have traditionally been considered less important on a rifle than on a pistol because rifles are not usually placed in a holster, a pocket, or a bag, the act of which can result in a foreign object engaging and actuating the trigger. In tactical situations, however, an operator may be more likely to quickly transition between use of a rifle and handgun and/or to allow the rifle to hang from a one or two point sling while performing some other close quarters task, such as reaching for other equipment or handcuffing a prisoner. If a chamber-loaded AR15-type rifle is allowed to hang from a sling with the manual active safety disengaged, it can and will discharge when any object presses the trigger, releasing the hammer. Unintentional discharge is an obviously serious consequence at any time and particularly when the firearm muzzle is not being safely controlled.